1. Field of the Invention
This invention relates to a combination radial tire for heavy load vehicles.
2. Description of the Prior Art
In tires generally used for heavy vehicles such as a large size truck, bus or the like under a heavy load, a tread portion of a so-called radial tire comprises a carcass reinforced by cord plies including cords arranged in a radial plane inclusive of a rotational axis of the tire or including cords inclined at a very small angle with respect to the radial plane. It is solidly reinforced by a belt composed of a plurality of metal cord layers, particularly a plurality of steel cord layers superimposed about the crown of the carcass and including cords inclined at a relatively small angle with respect to the circumferential line of the tire. The above mentioned radial tire mainly consists of a so-called all metal radial tire in which the above mentioned carcass is composed of one metal cord ply, more particularly one steel cord ply in the same manner as the belt.
Meanwhile, a so-called combination radial tire, in which one metal cord ply of the all metal radial tire is replaced by a plurality of organic textile cord plies, has recently been proposed.
The advantages and disadvantages of the all metal radial tire and of the combination radial tire balance each other. For example, the combination radial tire is lighter in weight and less expensive than the all metal radial tire. On the contrary, the combination radial tire comprises at least one bead portion reinforcing layer arranged outside the turn-up portion of the carcass and including cords, use may be often made of steel cords, and hence tends to easily induce a separation failure at the upper end of this reinforcing layer in the radial direction of the tire if compared with the all metal radial tire. In order to prevent such separation failure, a cover cloth including organic textile cords had heretofore been applied to the upper end of the bead portion reinforcing layer including steel cords. Such conventional a countermeasure, however, is not particularly effective. In addition, it is impossible to repair the separation failure induced at the above mentioned bead portion, and as a result, such separation failure is a vital defect inherent to the combination radial tire and hence has prevented the combination radial tire from being widely used.